1. Field of the Invention
The present general inventive concept relates to a side light-emitting device, a backlight unit that uses the side light-emitting device as a light source, and a liquid crystal display (LCD) apparatus employing the backlight unit.
2. Description of the Related Art
An LCD is a passive flat panel display that uses an external light source to produce an image. A backlight unit is used as the external light source and is located behind the LCD and emits light.
Backlight units can be classified as direct light type backlight units or edge light type backlight units according to a position of the light source. In the direct light type backlight unit, a plurality of light sources are disposed behind an LCD to directly emit light onto a liquid crystal panel. In the edge light type backlight unit, the light source is located along a sidewall of a light guide panel (LGP) to emit light onto the liquid crystal panel via the LGP.
The direct light type backlight unit may use light-emitting diodes (LEDs) as a point light source that emit Lambertian light. In order to prevent color light emitted from an LED from being directly visible above a diffusion plate when the light emitted by the LED is diffused by the diffusion plate and to illuminate the liquid crystal panel, a side-emitting LED is used to direct the light emitted by the LED to propagate into the diffusion plate in a direction that is slightly lateral.
U.S. Pat. No. 6,679,621 provides a side-emitting LED designed such that light generated by an LED junction is emitted from a side thereof by a conventional side emitter.
The conventional side emitter proposed in the above-cited reference includes a total reflecting portion and a refracting portion. That is, the conventional side emitter includes a funnel-shaped reflecting surface sloped with respect to a central axis thereof, a first refracting surface obliquely angled with respect to the central axis to refract light reflected from the reflecting surface, and a second refracting surface extending as a convex curve or sawtooth shape from a bottom surface of the conventional side emitter to the first refracting surface.
However, the sawtooth-shape side portion of the conventional side emitter is difficult to manufacture. FIG. 1 illustrates the conventional side emitter 1 (described above).
Referring to FIG. 1, the conventional side-emitter 1 includes the funnel-shaped reflecting surface 3 sloped with respect to the central axis c′, the first refracting surface 5 obliquely angled with respect to the central axis c′ to refract light reflected from the reflecting surface 3, and the second refracting surface 7 extending as the convex curve from the bottom surface 9 to the first refracting surface 5.
Light that is emitted from an LED (not shown) propagates into the conventional side emitter 1 and is incident on the reflecting surface 3. The light is reflected by the reflecting surface 3 to the first refracting surface 5 and is refracted by the first refracting surface 5 to exit the conventional side emitter 1 in a substantially lateral direction.
FIG. 2 illustrates an intensity distribution of light emitted from the conventional side emitter 1 in the side-emitting LED. As illustrated in FIG. 2, in the conventional side-emitter 1, not all light is emitted parallel to a horizontal axis and light that propagates along a path that is about 10° upward from the horizontal axis has the highest intensity. The light must be spread over a wider area in order to obtain a slim backlight unit and a uniform screen brightness. However, the side-emitting LED having the conventional side-emitter 1 does not satisfy this requirement.
Another drawback of the side-emitting LED having the conventional side-emitter 1 is that it is difficult to manufacture due to the complicated structure including the reflecting surface 3, the first refracting surface 5, and the second curved refracting surface 7.